The long term objective of this research is to understand the structure and function of dystrophin, the protein product of the Duchenne muscular dystrophy gene. The strategy proposed to attain this goal is to identify the cytoskeletal proteins which interact with dystrophin as well as with the dystrophin-glycoprotein complex in rabbit skeletal muscle. Five specific aims are proposed: First, the F-actin binding properties of purified dystrophin-glycoprotein complex will be studied. A cosedimentation assay will be used to quantitatively define the binding of native dystrophin-glycoprotein complex to F-actin binding properties of dystrophin-glycoprotein complex that has been disrupted by various dissociative agents will be determined using the cosedimentation assay to determine whether any other components of the dystrophin-glycoprotein complex modulate the interaction between dystrophin and actin or bind actin independently of dystrophin. Third, the role of the dystrophin- glycoprotein complex in crosslinking F-actin into bundles of networks will be assessed by light scattering and low-g sedimentation assays, as well as by electron microscopy. These experiments will determine whether classification of dystrophin in the actin binding protein family is appropriate. Fourth, this project will use blot overlay and affinity precipitation techniques to determine whether components of the dystrophin-glycoprotein complex interact with other cytoskeletal proteins using. The complementary approaches outlined will yield important new information about the cytoskeletal interactions of dystrophin and its associated proteins. Thus, the proposed research will provide insight into the pathogenesis of Duchenne, Becker and possibly severe autosomal recessive muscular dystrophies through the definition of the function of dystrophin by its interactions with other proteins in normal muscle. The results of this research will also aid in the rational design of fully functional dystrophin mini-genes for use in dystrophin replacement therapies.